Scientific diving techniques for the study of flooded sinkholes in Italy

The hydrogeology and geomorphology of some flooded sinkholes in central Italy have been studied by means of scientific diving techniques. A first group of three sinkholes is located on travertine deposits around the limestone ridge of the Cornicolani Mounts. One of these, S. Angelo Lake, is flooded by the outcrop of the regional water table. The other two, Regina Lake and Colonnelle Lake, are fed by geothermal springs with high levels of gas and are known as Acque Albule (white waters) because of the presence of cloudy layers of sulphuric water. It was possible to identify the S. Angelo Lake as a sinkhole created by the collapse of the roof of a former flooded cave. The underwater survey and water sampling of the Acque Albule sinkholes confirmed the presence of sulphuric springs emitting acidic water. The last studied sinkhole, Doganella sinkhole, is in the sedimentary cover of the Pontina Plain. It was created almost overnight by a sudden collapse in the unconsolidated sediments, and was then flooded by the local groundwater table. The S. Giovanni Lake can be classified as 'collapse sinkhole', while the Acque Albule are identified as hydrothermal-karst sinkholes. The Doganella sinkhole shows alluvial and piroclastic deposits in the submerged section, and its genesis is not totally understood yet.